Tread stock and method of making the same



I (if rubber from the li a which it is proposed to make.

Patented June: 24, 1930 1 f U IT Eo sTAn-is PATENT 0F wrnuau BURTON wnsco'rr, or

FICEQ DOVER, MASSACHUSETTS, ASSIGNOR TO RUBBER LATEX RESEARCH CORPORATION, OF BOSTON, MASSACHUSETTS, A CORPORATION or massadnuslrr'rs' ramp smoc Ami mm'non or MAKING THE SAME Ito-Drawing.

The present invention relates to a material adapted for use in the manufacture of various kinds of treads suchas rubber heels, rubber soles, tread for automobile tires and the like.- The objectof the invention is to produce a stock adapted for use by the usual vulcanizing processes in making rubber. heels, soles, tire treads and the like. The invention also consists in the method of making the stock.' To these ends the invention consists in the stock and method of making the same hereinafter described and particularly defined in the claims;

Heretofore fibrous material has been introduced into rubber compounds by milling operations. This, however, has resulted in destroying the staple, thereby shortening the fibre to such an extent as torender it practically valueless as a friction material. These fibres are practicallyreduced by the milling' operation to dust, and conferonly slight resistance to-slipping 6f the tread in use. I have discovered that fibre of such lengths as to be-available' for eificient use as a slipping preventative in treads may be introduced into a product without milling operation, and therefore .without the usual destruction of the fibre. The invention contemplates the use of comminuted rubber goods containing fibre such as worn out tire carcasses, rubber boots, rubber shoes and the like. The" material is comminuted in the ordinary manner which is practiced in reclaiming rubber, ofcomminuting the old material forms no vention.

Beginning, therefore, with the coniminuted rubber and fibre material, this material is more or less separated by blowing to divide the larger and" heavier particles fibre and rubber part of the present inton, and the cotton ust, so-called, consti-v tutes the principal ingredient of the stock is may rubberprincipally of conveniently be termed comminuted fibre material. It consists cotton to which is adherent particles of par-.

1tially" cured rubber, that is to say, rubber and the particular methodhter particles of cot Application filed March 28, 1924. Serial No. 702,697.

with asulphur content insuflicient to reduce the rubber to the condition of vulcanite, or hard rubber, when. subjected to vulcanizing heat and pressure. It also consists in particles of rubber to which small pieces of cotton are adherent. The rubber-fibre material consists of about 50% fibre and-50% partially cured rubber. This material is impregnated with fluid rubber latex by stirring the rubber-fibre materialinto the fluid rubber latex until the rubber-fibre material is substantially completely wetted, that is to say, until the particles-of rubber-fibre material are coated with fluid rubber latex.

The fluid rubber latex consists of the latex drawn from the been added alkali for the purpose of preventing coagulation, in which condition the fluid rubber latex is imported from the plantation. This' rubber latex is a fluid of varying composition, carrying emulsified iminute particles of rubber or material which becomes rubber after coagulationor passing through an irreversible solidification to a gel; When fluid rubber latex is dried down, without coagulation, it forms a gel containing, in addition to rubber, all the other solids dissolved and undis'solved of the orig inal latex. This dry latex gel differs in many ways from ordinary coagulated rubber. While any of the commercial grades rubber treelto which has of fluid latex maybe used to wet the comminuted rubber-fibre material, I find a .marked advantage inthe use of one which has been freed, as .far as; possible, of all its soluble non-rubber natural constituents such as carbohydrates, proteids, etc. The wet mixture of fluid rubber latex and rubberfibre material is poured in a mass upon a screen and vibrated to permit any excess of the fluid rubber latex to flow ofi. When the dripping of .fluid' rubber latex ceases the mass is'dried in cakes or slabs'of a thickness suitable for the particular form of tread in which it is to be used. The dried product ticles united by rubber gum, or, more properly ,speaking, latex rubber gel. The rubber-fibre particles constitute about 90% by weight of the stock,

9 is an adherent body of fibre and rubber ar-.

a small'percentage of pure 1 .and the gel material may be blanked out to form biscuit adaptedto be placed in a mold for making rubber heels or soles, or into blanks for use in making automobile tire treads, or

for any other purpose where a tread is de-- sired having alarge fibre content which will operate in use to prevent slipping of the tread on the surfaces with which it comes in contact. The stock is of a dark grayish color with white flecks appearin throu hout, which are larger pieces 0 the fibre 1 particles. The fibre in the stock has not, of

course, the staple of unreclaimed fibre such as cotton fibre, but it has a staple of suflicient length so that pieces of fibre are emf bedded in and held by the stock, and its ends go'to the surfaces where the materlal is subjected to wear. r

This tread stock is adapted to vulcamzation in' the ordinary manner in vulcanizing 1 presses, and when vulcanized the sulphur of but also with wet surfaces of pavement,

' wood and the'like. 1

The amount of pure gum or latex gel-introduced into thestock maybe var1ed by act ueous dilution. With a higher percentage 0 diluent, the amount" of rubber introduced into the stock is reduced, and conversely, with a less amount of water in the; fluid rubber latex, a higher percentage of will be introduced into the stock. The percent-.-

A age of gum may, therefore, be determined wlth great nicety' and with avoidance of waste, and only suflicient is used to secure the desired results without waste.

When the wetted mass of rubber-fibre material is drained of the fluid rubber latex no losses occur because the fluid rubber latex draining off is returned directly to the original body of the material without loss or m ury.

It'1s preferred to dry the rubber-fibre ma- *terial wetted with fluid rubber latex without com ression because the stock when formed in t 's manner is highly porous, and its drying is thereby fac1litated. In order to expedite the process, the excess of fluid rubber latex may be removed by centrifuging or by pressing, but the am in'time secured thereby is more than 9 time required in the drying operation. It is obvious that the stock must be thoroughly deprived of water before it is placed in the molds for vulcanizing. Therefore, unless special clrcumstances require themechanical about 10% by weight. This set by theadditional removal of the surplus fluid latex from the latex wetted' rubber-fibre material, it 1s performed without centrifuging or pressure operations.

In some instances, however, where the form of the blank or biscuit to be used in the manufacture of the tread is such as to permit, the process of preparing the biscuit may be expedited by centrifuging or pressure. For example; it is proposed to produce biscuit for use in the manufacture of heels by expressing part of the excessive fluid latex by pressure and then extruding a rod of a cross-section corresponding to the shape of the proposed rubber heel blank, and after the rods are dried, cutting them transversely to-form'heel biscuit, WhlCh are then compressed. Y

An important characteristic of the method consists in the uniting of particles of fibre and partially cured rubber by means of a filmiform deposit of rubber gel from fluid rubber latex, the rvulcanization of the uniting film being accomplished by the utilization of the sulphur in the rubber-fibre material. Additional sulphur, or otherlvul- 'a formsuch-as to be introduced into the mold cavities, and until placed in the mold and subjected 'to' heat to retain its form, and yet when subjectedto heat and pressure to flow into and fill the mold cavity, and there- .fore it is adapted to convenient use in mak in% molded rubber treads. a he fibre content of the rubber-fibre material may be increased or decreased, de-

pending upon the abrasive resistant characteri'stics desired in the product to be made from the stock. The least expensive stock will be formed of fibre stock towhich are adherent particles of rubber without addition of fibre just as it comes from the rubberfibre separation of the comminuted raw materials, In some cases, how'eyer, it may be desired to add more fibre, and for this purpose pure fibre may be employed in order to increase the-percentage of fibre and the abrasive resistant ua-litles of "the product made from the stoc On the other hand,

if it is desired to producer a tread having greater resiliency than that secured by treating the fibreroduced from the blowing process, an ad ed quantity of comminuted partially cured rubber may be used.

If it be desired to produce a stock of a particular color, water" soluble dye, preferably with an adsorptive filler may be use'd desired color in the stock.

in the fluid rubber latex or pigmentous ma terial may be added thereto to produce the Having thus described the invention; what is claimed is:

1. The method of making tread stock which consists in mixing and surrounding comminuted, partially cured rubber-fibre particles with alkaline fluid rubber latex in relatively small proportion compared to the Weight of rubber-fibre material, and dryin the mixture without coagulation of the latex to form an interstitial gel uniting the rubber-fibre particles.

2. The method of making tread stock which consists in wetting partially cured rubber particles and fibre with an excess of alkaline fluid rubber latex, removing the excess of fluid and drying the material with: out coagulation of the latex to form an interstitial gel uniting the rubber-fibre par ticles.

3. As an article of manufacture, a rubber fibre tread stock consisting of particles of partially cured rubber and fibre united by interstitial latex rubber gel.

4. The method of making tread stock which consists in wetting partiall cured rubber particles and fibre with alkaline fluid rubber latex substantially free from soluble I non-rubber natural latex constituents and drying the material without coagulation of the latex to form an interstitial gel uniting the rubber-fibre particles.

5. As an article of manufacture, a rubber fibre tread stock, consisting of particles of partially cured rubber and fibre united by interstitial latex rubber gel substantially; free from soluble non-rubber natural. latex constituents.

6. As an article of manufacture, a rubber fibre tread stock consisting of particles of partially cured rubber and fibre constituting the major portion of the weight of the article, and interstitial latex rubber e1 surrounding and uniting the particles 0 rubber and fibre.

7. The method of making tread stock which consists in mixing and surrounding comminuted, partially cured rubber-fibre particles with alkaline fluid rubber latex, and drying the mixture without coagulation of the latex to form an interstitial gel uniting the rubber-fibre particles.

In testimony whereof I have signed my name to this specification.

WILLIAM BURTON WESCOTT. 

